1. 11 Feb, 2008 1 commit
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    • hezx@mail.hezx.com's avatar
      update test result · 7572a9e3
      hezx@mail.hezx.com authored
      7572a9e3
    • hezx@mail.hezx.com's avatar
      BUG#26489 Corruption in relay logs · e4f37eab
      hezx@mail.hezx.com authored
      Here is the scenario that causes the failure.(by Mats)
      
      1. The to-be corrupt log event (let's call it X), is split into two
         packets B and C on the network level (net_write_buff()). The parts
         are X = (x',x''). The part x' ends up in packet B and part x''
         ends up in packet C. Prior to the corrupt event X, the event Y has
         been written successfully, but has been split into two packets as
         well, which we call (y',y'').
      2. The master sends packet A = (y'',x') to the slave, increases the
         packet sequence number, the slave receives the packet, but fails
         to reply before the master gets a timeout.
      3. Since the master got a timeout, it reports failure, and aborts
         sending the binary log by exiting mysql_binlog_send(). However, it
         leaves the buffer intact, still holding y'' (but not x', since the
         write_pos is not increased).
      4. After exiting mysql_binlog_send(), the master does a
         disconnection of the client thread, which involves sending an
         error message e to the client (i.e., the slave).
      5. In this case, net_write_buff() is used again, but this time the
         old contents of the packet is used so that the new packet is
         D = (y'',e). Note that this will use a new packet sequence number,
         since the packet number was increased in step 2.
      6. The slave receives the tail y'' of the Y log event, concatenates
         this with x' (which it already received), and writes the event
         (x',y'') it to the relay log since it hasn't noticed anything is
         amiss.
      7. It then tries to read more bytes, which is either e (if the length
         given for X just happened to match the length given for Y, or just
         plain garbage because the slave is out of sync with what is
         actually sent.
      8. After a while, the SQL thread tries to execute the event (x',y''),
         which is very likely to be just nonsense.
      
      The problem can be fixed by not resetting net->error after the call of 
      mysql_binlog_send, so the error message will not be sent and the connection
      will be closed.
      e4f37eab
  8. 27 Jan, 2008 3 commits
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  11. 23 Jan, 2008 2 commits